The present invention relates generally to signal spectrum display apparatuses and more particularly to a signal spectrum display apparatus in which the real-time level display, the holding level display, and the like can be selectively carried out, respectively, on a display panel by a simple switch operation.
In general, in the recording of an audio signal, it is desirable in some instances to carry out the signal recording with the levels of the desired frequency bands in which these signals exist in lowered or raised state. In the reproducing apparatus, furthermore, in the case where the fidelity of the reproduced audio signal is impaired by the effects of characteristics such as the frequency characteristics possessed by the speakers, pickup cartridge, and other acoustical devices themselves and the transmission characteristic of the listening room, it is desirable in some instances to correct the levels of signals of certain frequency bands. In addition, there are instances wherein, for both recording and reproducing, the frequency characteristics are not made flat but are transformed into desired characteristics. In such cases, a graphic equalizer capable of variably adjusting signal level is used for each of the divided frequency bands.
For adjusting the level in the graphic equalizer of this type a signal spectrum display apparatus is used, which displays the level of the input signal in all bands, and the signal levels in different frequency bands.
However, since the level of the input signal varies from time to time, moment by moment, it is considerably difficult to accurately perceive the state of the level at a certain instant of time. Accordingly, in order to perceive the state of the level at any one instant of time, it is necessary that the display of the state of the level at that instant be stopped. Thus, in a known spectrum display apparatus, the input signal is shifted by means of a shift register of 100 bits, for examply, and this is digitally held and supplied to a display drive circuit thereby to carry out level displaying for each of the divided bands.
This known spectrum display apparatus has disadvantages in that it simply displays the input signal level at real-time, or displays the held and stopped signal level, thus not being able to display the maximum level of the input signal spectrum. Furthermore, a man cannot know the tendency of the frequency characteristics of the input signal.
In this known apparatus, the stopping of the level display is accomplished by holding the shift register. For this reason, after the level display has been once stopped, this state of display is preserved. As a consequence, when normal displaying in accordance with the level variations occuring from time to time, moment by moment is resumed, it has been necessary to terminate the stopped state of the display by operating a switch each time. For this reason, the operation of the apparatus has been very troublesome. Furthermore, since a shaft register is used in this known apparatus, in the case where the number of the display elements is increased in order to display the level state in an even finer manner, the number of bits of the shift register must be increased, and problems such as higher cost of production arise.